During well operations equipment can become lodged in a well bore and simply pulling on the stuck object will not release it from the retained position in the well. In order to loosen stuck objects, jarring devices designed to impact a sudden force are used in conjunction with fishing tools such as spears or overshots that are attached to the objects.
The usual jarring tools utilize a latch means depending upon its resiliency or an associated resilient means to maintain the means in latched position. Upon a predetermined upward tension applied to the jarring tool, the resilient force holding the latch means in place is overcome and the latch means is disengaged from its latched position. In the case of a latch means formed by spring-like collet fingers, the fingers are subject to constant flexing which results in fatigue and loss of elasticity, whereby the fingers become ineffective after a relatively short period of use. Also, the collet fingers include latching shoulders which are relatively small and become worn to the extent that their holding ability is greatly decreased.
Other types of latch means, such as ball detents have been used but here again, the holding balls are subjected to constant wear which decreases their effectiveness. Such ball detents have the additional disadvantage of being difficult to mount and maintain in position in annular carriers, and experience has shown that balls become dislodged from their carrying position and jam the tool or are completely displaced and lost. Examples of such prior jars are shown in U.S. Pat. Nos. 3,406,770 and 3,203,482.